1. Field of the Invention
This invention generally relates to a ball spline bearing assembly, and, in particular, to improvements in such a ball spline bearing assembly.
2. Description of the Prior Art
A ball spline bearing assembly is well known in the art. A typical prior art ball spline bearing assembly includes a spline shaft formed with at least one spline groove at its peripheral surface extending in parallel with the longitudinal axis, an outer sleeve fitted onto the spline shaft with a predetermined gap therebetween and a plurality of balls interposed between the spline shaft and the outer sleeve to provide a rolling contact therebetween. The outer sleeve is typically provided with at least one endless circulating path along which the balls circulate endlessly so that the spline shaft may move relative to the outer sleeve in the longitudinal direction. Such a typical ball spline bearing assembly is useful in many applications; however, it tends to be bulky since an endless circulating path must be formed in the outer sleeve, and, moreover, it tends to be expensive due to difficulty in manufacture. Furthermore, since the balls are physically in rolling contact with both of the spline shaft and the outer sleeve, the resistance between the spline shaft and the outer sleeve is relatively large, which tends to hinder a fine relative positional control between the spline shaft and the outer sleeve.
In a typical prior art ball spline bearing assembly, the distance between the outer surface of the spline shaft and the outer surface of the outer sleeve is required to be set approximately at twice the diameter of the balls used, and, thus, if such a ball spline bearing assembly were to be fabricated compact in size, difficulty would be encountered in manufacture since enough space could not be found easily in designing an endless circulating path. Because of recent expansion of application of robot machines in various fields, there has been a need to develop a ball spline bearing assembly compact in size and high in performance.
One such prior art ball spline bearing assembly is disclosed in the Japanese Utility Model Post-examination Pub. No. 1-39939. In this ball spline bearing assembly, a plurality of threaded radial holes are provided in the outer sleeve arranged longitudinally as well as circumferentially at equal intervals and a ball holder having a substantially spherical concave end at its inner end is threaded into each of the radial holes. And, a ball is rotatably received in the concave end of the ball holder and the ball is partly exposed and received in a corresponding spline groove of the spline shaft. Thus, a rolling contact is provided between the outer sleeve and the spline shaft through the balls, so that there may be provided a relative linear motion between the outer sleeve and the spline shaft.
However, in the prior art ball spline bearing assembly, since it is so structured that lubricant oil is supplied to the balls from an oil groove formed at the outer surface of the outer sleeve through an oil supply hole, there is a difficulty in keeping the spline grooves and the balls lubricated uniformly at all times.